Stabilization of formaldehyde solutions



Patented Apr. 1, 1941 STABILIZATION OF FORMALDEHYDE SOLUTIONS Robert C. Swain, Riverside, and Pierrepont Adams, Stamford, Coma, assignors to American Gyanamid Company, New York, N. Y., a com-- ration of Maine No Drawing. Application November 28, 1939, Serial No. 306.516

3 Claims.

This invention relates to the stabilization of formaldehyde solutions by the addition thereto of compounds capable of preventing polymer formation.

It is well known that aqueous formaldehyde solutions of greater than about 30% strength such as, for example, ordinary U. S. P. formalin of 37% strength are unstable upon storage, particularly at low temperatures, as they will pre-' cipitate formaldehyde polymers. For this reason it has been customary to add methanol to such solutions as a stabilizer.

For some uses, and particularly for the manufacture of aminoplastics, formalin solutions containing alcohols are undesirable. For this reason, urea, thiourea and other simple organic nitrogen compounds have been suggested as substitutes. While these materials and particularly urea are effective to stabilize U. S. P. formalin solutions for considerable periods of time they are not altogether satisfactory for the more concentrated formaldehyde solutions.

We have now discovered an effective class of stabilizers for aqueous formaldehyde solutions consisting of melamine and alkylol melamines, particularly methylol melamines. member of this class, which is melamine itself,

The preferred can be used in concentrations of 2-6% by weight to stabilize aqueous formaldehyde solutions up to about 45% by weight and in these low concentrations there is no danger of gel formation. Alkylol melamines such as the hexamethylol melamine formed by condensing one mole of melamine with 6 moles of neutral or slightly alkaline formaldehyde are effective in concentrations of 2-5% by weight for stabilizing aqueous formaldehyde solutions of 37% strength or less. These materials will also stabilize stronger formalin solutions such as 42% aqueous formaldehyde, particularly when used in concentrations higher than 5%, but the solution sometimes becomes cloudy upon refrigeration.

It is known that strongly acid formalin solutions, and particularly solutions having a pH of about 3-4, are more easily stabilized than those which are only slightly acid. We have found that this is also true of formalin solutions stabilized with melamine and alkylol melamines; the solutions require smaller amounts of stabilizer and remain clear for longer periods of time at pH values of 3-4 than at higher pH values. However, our invention is not limited to the stabilization of strongly acid formalin solutions as we have found that our new stabilizers are ef ective in many cases at pH values higher than 7.0.

In practicing our invention we prefer to dissolve or disperse the melamine or alkylol melamine in the formalin solution at room temperatures or, when more rapid stabilization is desired or when .concentrations of stabilizer higher than 5% are used, as in treating 45% formaldehyde solutions, at slightly elevated temperatures. After the solutions are stabilized they may be stored, shipped, or treated in any suitable manner without regard to temperature conditions as they are stable even at temperatures as low as 0 C. It is a further advantage of the invention that melamine and alkylol melamines will also stabilize the formaldehyde solutions against excessiveoxidation to formic acid.

As has been indicated, our discovery is of particular value in the preparation and storage of formalin solutions for use in the manufacture of aminoplastics such as melamine-formaldehyde and urea-formaldehyde syrups, lacquers and resins. Compositions of these syrups have greatly improved properties, especially in respect to water resistance, when made from alcohol-free formal- 'dehyde.

The invention will be illustrated in greater de-. tail by the following specific examples, which show the results obtained with various materials representative thereof. It is understood, however, that although these examples may describe certain of the more specific features of the invention they are given primarily for purposes of illustration and the invention in its broader aspects is not limited thereto.

Example 1 Since unstabilized solutions of formaldehyde greater than 30% concentration were not obtainable commercially, solutions suitable for testing were prepared from 30% methanol-free formalin by vacuum concentration. The 30% formalin solution was heated at 25-30 C. at 1-5 cm. of mercury pressure until the requisite amount of water had been removed, after which the exact for an additional Remarks before refrigeration. cl. before refrigeration.

Rermrb v cloud cry Clear. y 1

Do. Cloudy gel alter 4 (in Clear at and of test. ys'

Do. 80in. v. sl. cloudy before refrigeracloudy before refrigeratlon.

tron. Solnbwarmed to dissolve stabilizer.

Clear at end at test.

Very cloudy after 1 day.

911 after 2d month 2:3 V slight! loud 5. 70 Ca. y

6. 1) Cloud ii. 15 Very nightly cloudy.

Example 2 3.32 Clearatendoi test. ass

3. 48 Clear at end of test.

3.47 Solo. sl. cloudy beiore reirlgerr 3.60 Boln. v. sl. cloudy before refrigera- 3.41 80111. warmed to dissolve stabilizer.

The results obtained were as Neutralto pH After the second month's storage the awmmnwum aaaaaaaa melamine without gelation.

Aqueous formaldehyde solutions were prepared added until the pH was 'I or higher and the solumonth. soiutionswere examined and their pH was again noted at follows OHIO .unuummmu andstabilizedasinExample1andstoredat4 C.for1month. 'I'heywere then warmedto25 C.,' the pH was taken, sodium hydroflde was 19 tions were again stored at 4 4days 14 day l8days 29days 3hrs.- 14dsys-.

Percent 4 days-.. 2 days... %dsys 14 days Stabilizer mdnya. 4

1 day 3 days 14 days 4 days--. 14 days 29 dsys 7 hrs- 32days 4 Ndays auunwmmmwwuunuuuu Percent 011:

oa-bm-b znl ummlnaslzsz The results obtained are indicated in the following table:

Stabilizer These results show that melamine acts as a strong stabilizer for methanolfree formaldehyde stronger formaldehyde solutions the mixture was solutions it is possible to use as much as 10% of warmed or heated to acceleratesohttion of the I stabilizer. The were then placed in a reirigeratorand cooiedtothetemperatures noted.

afterwhich theywere observed every few hours 5 during the first day and at lessfrequent intervalsthereafteri'oronemonth. At theend ofthis timethesolutionsthatshowedverylittleor no precipitation of paraformaldehyde were tested forpH readings.

Hammethylol melamine. I

None

I Do"--- mum solutions over a wide range of formaldehyde concentrations. However, as a practical ma w a u m d m a mmm v m Wm mum m mum mm MW mm mm m. a mm mm m should be noted that the amounts of melamine tion at low temperatures under both neutral and tobeusedarelimitedintwoways. Atany chosen concentration of formaldehyde and temperature of refrigeration a certain minimum What we claim is:

1. An aqueous formaldehyde solution having a formaldehyde content of at least 35% and which is otherwise unstable on storage at low temperatures and containing stabilizing amounts within melamine. This working range will be desisthe range or 140% of a compound selected from nated as stabilising amounts of the stabilizer.

2. An aqueous-formaldehyde solution having a formaldehyde content of approximately 44% and formaldehyde solutions, but with thefstrongest containing stabilizing amounts within the muse tage of the invention.

' the group consisting of melamine and methylol melamine.

quantity of melamine is n to inhibit the prqipitation of formaldehyde polymers and 65 above a certain percentage of melamine a precipitation of melamine-formaldehyde condensation products or gelatin takes place. The same is true of alkylol melamines such as hexamethylol Reference to the table will show that 14% of melamine will entirely stabilise 35-40% formaldehyde solutions and 34% will stabilize 40-45% of 540% of a, compound selected from the group consisting of melamine and methylol melamine.

3. A method of stabilizing an aqueous tormaldehyde solution of at least 35% strength which range of 140% of a. compound selected from the group consisting amine.

of melamine and methylol mei- ROBERT C. SWAIN. PIERREPONT ADAMS.) 

